1. Field of the Invention
This invention relates to inclinometers. Inclinometers are used for measuring the angle of displacement of a body or structure relative to the vertical.
2. Description of the Prior Art
Inclinometers normally comprise a casing and a mass which is movably supported relative to the inclinometer casing. The mass is usually a pendulum, so that when the inclinometer casing is rotated about a horizontal axis, the pendulum tends to remain vertical, and consequently there is a relative angular displacement between the pendulum and the inclinometer casing. By measuring this relative displacement directly or indirectly, the inclination of the inclinometer casing, and therefore of a structure to which it is attached, can be determined.
If the inclinometer is subjected to mechanical vibration, the pendulum may begin to oscillate about the pendulum swing axis. Such oscillations may become particularly large when the frequency of vibration has a similar value to that of the pendulum swing frequency. To reduce this problem, the pendulum is usually damped relative to the inclinometer casing. That is, relative movement between the pendulum and the inclinometer casing is used to dissipate the kinetic energy of the oscillating pendulum is heat, for example using friction or by first converting the kinetic energy into electrical energy and then dissipating the electrical energy as heat in a resistance. Throughout this specification the term "damping" is used to cover any suitable means for dissipating the kinetic energy of oscillation as heat energy. Also throughout this specification the term "pendulum swing axis" means the axis about which the total pendulum assembly can be considered to be rotating at any instant in time. In the case of a simple pivoted pendulum, the pendulum swing axis is the axis of the pivot, but in a more complex support the position of the pendulum swing axis could vary with time.
When damping is provided, any change in the inclination of the structure to which the inclinometer is attached still results in a relative movement between the pendulum and the inclinometer casing, but the effect of the damping is to impart a force to the pendulum, displacing it from the vertical. As a consequence, when the change in the inclination has ceased, the pendulum returns to its vertical position, but this vertical position is only reached after a period of time has elapsed. Consequently, the response rate of the inclinometer is determined by the settling time required for the pendulum to return to the vertical and such inclinometers cannot be used in dynamic applications where a fast response rate is required.
Conventional inclinometers normally comprise a single pivot with a horizontal axis from which is suspended a mass on some form of rigid link to form the pendulum. The shape of the link may be geometrically complex and may provide some of the pendulum mass. Horizontal oscillations of the pivot axis can result in the centre of gravity of the mass tending to remain stationary, and an angular rotaion being imparted to the pendulum. Therefore horizontal oscillations of the pivot axis result in angular oscillations of the pendulum and consequent loss of stability of the inclinometer output signal.